<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        .bg{
            widows: 100px;
            height: 100px;
            background-color: red;
            /*盒子阴影
            box-shadow:offsetX:水平 offsetY:垂直 blur:高斯模糊 size:背景尺寸 color:颜色
            */
            box-shadow: 10px 20px 5px 7px #333;
        }
    </style>
</head>
<body>
    <div class="bg">

    </div>
</body>
</html>